Steam is often used in industrial processes. For example, steam can be used for heat exchange, as a power source for driving turbines, etc.
In the petroleum industry, for example, a particular application is for the generation of steam for the recovery of bitumen or heavy oil. A common process utilized for the in situ recovery of heavy oil or bitumen is to inject steam underground pursuant to which the viscosity of bitumen or heavy oil is decreased such that it flows and is capable of being pumped to the surface. For this, steam generation apparatus commonly called steam injection boilers (“SIB”) are used to generate steam of the required/desired quality or quantities. These boilers are typically fired with natural gas (which is piped to the boiler) in order to heat water to generate the desired steam.
The current art typically uses natural gas as the fuel to fire most oilfield steam generation boilers. For in situ recovery of bitumen or heavy oil, prominent processes utilized are steam assisted gravity drainage (“SAGD”) and cyclic steam stimulation (“CSS”). The SAGD process is presently the most commonly used process for recent and new projects due to its enhanced efficacy in the recovery of bitumen or heavy oil. Generally, 80% quality steam is required/desired to be generated by the boiler in specified volumes per hour depending on output capabilities of the boiler, as well as steam output requirements for the recovery and extraction process. Exceeding 80% quality renders a project uneconomical, largely due to water treatment costs. Conversely, lower than 80% quality steam introduces inefficiencies to the process utilized for heavy oil or bitumen recovery and, hence, is also undesirable from a cost-effectiveness perspective. Typically the quality of the steam will degrade as heat exchange surfaces foul over the run time of the equipment.
Typical problems generally encountered under conventional steam generation boilers include (but are not limited to):
(a) failure to maintain 80% quality steam (or such other quality of steam as required or desired) at the outlet of the boiler—often lower quality steam is generated; and
(b) cost of fuel, typically natural gas, to fire the boilers used for steam generation (plus the cost of associated pipeline construction and maintenance to bring the natural gas or other fuel to the boiler).
In addition, problems typical for pipeline transport of produced bitumen include that the availability and handling of diluent increases the overall cost of transporting the bitumen to upgrading facilities, pipelines are required to return diluent to the production facility, and electrical power required at the production facility and pipeline facilities often requires expensive transmission lines from the power host or supplier.
It has been proposed previously to convert to other fuels so that propane or light fuel oils could be utilized to fire the boilers instead of natural gas. However, as with natural gas, a source for the propane or light fuel oils would need to be located nearby in order to be piped to the boiler, thus increasing costs. Moreover, the heat input to the boiler will change due to the difference in the energy density of the new fuels, resulting in a drop in the steam quality and/or the production of less steam and, in turn, less heavy oil or bitumen being produced. Liquid fuels will create a longer flame, in other words, of different shape than that for which the combustion chamber was designed and built to accommodate. As such, existing boilers will have to be derated such that existing fire boxes can be utilized to accommodate the differently shaped flame when liquid fuel is used.
Moreover, an alternative processes which utilize solvents instead of steam to reduce the viscosity of heavy oil or bitumen is presently being employed for the recovery and extraction of heavy oil and bitumen. However, while possessing the advantage that it does not require natural gas for firing the boiler or for that matter the boiler (and related ancillary equipment) or the water which is heated to create steam, still must overcome a significant cost disadvantage relative to the SAGD and CSS processes for recovering and extracting heavy oil or bitumen.
Canadian patent application No. 2,419,617, published Aug. 21, 2004, teaches a method for enabling the use of a “heavy oil residuum” by converting it to a useful product. The method involves the use of a heavy oil residuum which is substantially non flowable. The viscosity of the residuum is reduced by the application of heat and use of a diluent. This method appears to suggest the use of a diluent to reduce viscosity of the residuum, and the making of an emulsion with the heavier residuum, and subsequently with water, and then burning the resultant product to produce energy as heat. The burning of the residuum emulsion results in a net energy contribution from the residuum's combustion.
United States Publication no. US 2005/0218037 published Oct. 6, 2005, teaches a system for heating multiphase residues containing water, oil and solids to obtain hydrocarbons and other useful products. This system comprises a tubular reactor provided with a fixed pitch screw conveyor where the multiphase residue is heated under reduced pressure and in the presence of an inert gas, the heating being carried out in distinct temperature zones with a first zone of evaporation of free and emulsified water and extraction of light hydrocarbons, a second zone of thermal desorption and a third zone of mild pyrolysis, the various hydrocarbon fractions being collected in condensers at the relevant stages, while the solids are separated for post-treatment and industrial use.